This invention relates to a mechanism in the wheel end of a vehicle for shifting the wheel between driven and non-driven states and more particularly it relates to the manner of maintaining the predictability of such shifting.
Recent developments in four-wheel to two-wheel drive shift mechanism provides for clutch ring shifting inboard of the vehicle""s knuckles at the front end of the vehicle. (See commonly assigned U.S. Pat. Nos. 6,170,628 and 6,234,289) A typical arrangement is one where a pneumatic annular actuator is mounted between the knuckle and the CV-joint. The actuator slidably moves a clutch ring for engagement and disengagement as between the CV-joint and the wheel hub of the vehicle. The actuator by its mounting produces a seal surrounding the inner cavity containing the clutch ring and associated components which are accordingly protected from contamination. The actuator produces actuation by axial movement of a flexible wall forming one side of an annular vacuum chamber. The flexible wall is exposed to the cavity and is connected to the clutch ring for moving the clutch ring and thus producing engagement and disengagement.
The sealing of the cavity provides a valuable function by keeping out dust and moisture that are contaminants that can interfere with the functioning of the shift components. That same seal, because it provides air tight sealing, can be disruptive of the shifting function. The area of the vehicle whereat the cavity resides is subjected to dramatic changes in temperature during normal operation of the vehicle. Elevation differences may also have an affect and even the axial movement of the movable wall which changes the cavity volume produces pressure changes. Whereas the sealing of the cavity is necessary to avoid contamination of the components (clutch ring, fork, bearings, etc.), the pressure changes within the cavity inhibits or enhances the expansion of the air chamber to negatively affect the predictability of the shifting force. An objective of the invention is to provide venting of the cavity to avoid pressure changes within the cavity but without allowing contamination of the cavity.
A solution to the above problem is to provide a special vent including an air line that is open to ambient air at a location where the air is not contaminated. This amounts to providing a passage at some point through the cavity wall, connecting an air line to the passage and extending the air line to a location where there are no contaminants, e.g., in the engine compartment of the vehicle.
As contemplated herein, a rotating CV-joint is located in close adjacency to a rotatively fixed knuckle. The annular actuator is mounted to the knuckle and includes a rotary seal that is in abutting relation with the rotating CV-joint and which prevents passage of air/contaminants between the actuator and the CV-joint. The CV-joint does not lend itself to attachment to a fixed air line and drilling a hole through the knuckle is undesirable for a number of reasons. The annular actuator is essentially an outer fixed ring and an inner expandable ring that form opposing walls of the expandable air chamber. An air line extends through the fixed wall and into the expandable chamber to provide controlled pressurization of the chamber and thus axial movement of the inner wall. A passage cannot be provided through the air chamber and the assembly of the three components (CV joint, knuckle and actuator) does not appear to lend itself to any form of venting.
The present invention nevertheless provides the venting of the cavity through the actuator but without breaching the air chamber. The metal ring forming the outer wall of the actuator is U or cup shaped. An inner elastomeric ring mates to the metal ring and provides the movable wall that expands into the sealed cavity whereat the clutch ring resides. In the prior actuator, a boss was provided integral with the metal ring and a hole or passage was drilled through the boss and through the metal ring and into the chamber. A vacuum tube extended from the hole in the boss to the intake manifold for pressurization of the chamber. The outer side of the ring is provided with the rotary seal that seals against the rotating CV-joint and creates the sealed cavity at the inner side of the actuator. The boss of the present invention is configured to overlap this rotary seal. A second passage or hole is drilled through the boss (and not through the metal ring) to the juncture whereat the rotary seal is attached to the metal ring. An annular groove is formed in the ring at the juncture and intersects the vent passage whereby exterior air can pass through the vent passage and into the groove. At least one slot and preferably several slots extend from the groove inwardly and behind the seal to the sealed cavity. An air line is connected to the passage and extends to a position where contamination is not a problem.